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The resuscitated fetal human heart can be used as an experimental tool for the investigation of the excitatory process in the human heart. During perfusion the configuration of the epicardial electrocardiograms does not change appreciably. For accurate recording permitting a detailed analysis, the use of a high-fidelity oscillograph is absolutely necessary, otherwise no identification of the rapid portion of the intrinsic deflection can be made. The heart is suspended in an homogenous volume conductor at 37 C. and perfused with fluid matching as closely as possible the composition of the extracellular fluid. The morphology of the unipolar complexes is difficult to describe adequately. At the anterior side of the right and left ventricles rS complexes are found. Some parts of the left ventricular wall and posteroapical region of the left ventricle show QR complexes. In the area bordering the A-V groove one-third the distance from apex to basis, deep Q waves and even QS complexes are found. The relatively late intrinsic deflection here points to late excitation of this region. In regions neighboring the A-V groove, the Q wave diminishes in size and the R increases. The left posterior part of the left atrium is activated latest in the atrial cycle. The epicardial excitation pattern is surprisingly simple. The excitation wave reaches the region of attachment of the right anterior papillary muscle first, then spreads radially with varying velocity across the left ventricle towards the posterobasal region, while another wave spreads simultaneously across the right ventricle towards the same region. There is, therefore, a double envelopment of the epicardial surface. A comparison of the complexes having an intrinsic deflection occurring at the same time shows conclusively that, even over the same ventricle, the morphology of these complexes may be completely different. Thus the excitation time does not determine the morphology of the complexes. There is no typical right or left ventricular pattern. There appears to be no relationship between thickness of the heart wall and height of the R wave.

Epicardial Excitation Pattern as Observed in the Isolated Revived and Perfused Fetal Human Heart